Typically, starch is subjected to thinning action by mineral acids and by oxidative thinning with sodium hypochlorite. The object of these thinning methods is to obtain a starch having modified viscosity characteristics, but not so completely thinned that it is water soluble. Such reactions are usually performed on the granular state, and usually in a slurry suspension. The starch products resulting from the slurry reaction are conveniently filtered and washed to remove water soluble impurities and salt resulting from the reaction.
There are two problems associated with acid thinning and sodium hypochlorite oxidative thinning. At the present time, mineral acids and sodium hypochlorite are in short supply due to chemical shortages. In addition, both of these processes inherently generate inorganic salts which are discharged as effluents from the starch processing facility. In some cases, the cumulative effect of all sewage effluents from a manufacturing facility may exceed the amount permissible by law. In such cases, it is desirable to limit such effluents where practical to permit a greater volume of manufacturing of other products in which effluents cannot be avoided.
Since both mineral acid thinning and sodium hypochlorite oxidative thinning result in organic and inorganic salt by-products, which do increase the effluent load for a manufacturing facility, a search was made to find another means of accomplishing the thinning desired for a particular starch derivative, and which would minimize the amount of by-product salts which would be discharged into the sewer. This investigation led to the consideration of the use of hydrogen peroxide as an oxidative thinning agent.